1. Field of the Invention
The present invention relates to a magnetic disk apparatus for performing records on a magnetic disk with a high density.
2. Description of the Related Art
A magnetic disk apparatus in recent years has a tendency of becoming smaller in size but larger in capacity. For this reason, there is made an attempt to improve a recording density of the magnetic disk, i.e., a track density and a bit density. For improving this bit density, in place of a conventional readable/writable inductive head, a magnetic reluctance head (MR head) capable of taking a larger level of a regenerative signal is utilized as a reading head. Hence, the magnetic head involves the use of two heads, i.e., the inductive head for writing and the MR head for reading.
Such two heads are different from each other in terms of their positions in a track direction, and, therefore, a problem is a decline of a follow-up capability along the tracks due to a skew of a shaft and an angle of rotation relative to a rotary actuator.
FIG. 57 is a view illustrating a construction of a magnetic disk apparatus in the prior art. FIG. 58 is a characteristic diagram of a head position versus a yaw angle in the prior art. FIGS. 59A, 59B, 59C and 59D are diagrams of assistance in explaining the yaw angle in the prior art.
As depicted in FIG. 57, an actuator 92 moves a magnetic head 93 in its radial direction with respect to a magnetic disk 90 rotating about a center-of-rotation 91. This actuator 92 involves the use of a rotary actuator rotating about a center-of-rotation 94, thereby attaining down-sizing of the apparatus.
An MR head capable of enhancing the bit density is used as a read head of this magnetic head 93. As shown in FIGS. 59B and 59D, if this MR head is used as a read head 93-2, it is required that a write head 93-1 be provided separately. For example, the inductive head is employed as the write head 93-1. Thus, it follows that a gap position between the individual heads 93-1 and 93-2 of the magnetic head 93 differs.
This rotary actuator 92 rotates about the center-of-rotation 94 and thereby moves the magnetic head 93 in the radial direction of the magnetic disk 90, and, hence, a locus thereof depicts a circular arc. Accordingly, an angle (head skew angle or yaw angle) with respect to the track (cylinder) direction of the magnetic head 93 is not 0.degree.. Besides, a yaw angle on the inner side of the magnetic disk 90 becomes as shown in FIGS. 59A and 59B. On the other hand, a yaw angle on the outer side of the magnetic disk 90 turns to be an angle as illustrated in FIGS. 59C and 59D. Consequently, the yaw angle changes on the inner and outer sides of the magnetic disk 90.
Take the construction of FIG. 57A for example, a distance Rcg from the center-of-rotation 94 of the actuator 92 up to the gap position of the magnetic head 93 is set 0.85 times as small as a distance Rsc from the center-of-rotation 94 of the actuator 92 up to the center-of-rotation 91 of the magnetic disk 90. As illustrated in FIG. 58, the variation in the yaw angle at this time amounts to a value as large as 24.degree..
This yaw angle causes a deviation between the write head 93-1 and the read head 93-2 with respect to a cylinder locus. This results in a narrowed effective gap width of the read head 93-2 and, consequently, a decline in terms of a read characteristic. For this reason, it is desirable that both the yaw angle and the variation in the yaw angle be small.
As a method of reducing an absolute value of this yaw angle, Japanese Patent Laid-Open Publication No.4-232610 proposes a method of shifting the positions of the heads 93-1, 93-2. Further, there is proposed another method of decreasing the yaw angle by using an actuator having a fan-shaped bearing (see Japanese Patent Laid-Open Publication No.2-126497).
Also, there are some configurations of a conventional disk enclosure, wherein a base and a cover are separated up and down, and the base and the cover are separated right and left (see Japanese Patent Laid-Open Publication No. 4-232610).
The conventional apparatus which effects the read/write processes through the same element presents no problem because of causing no track deviation due to the yaw angle. As shown in FIGS. 59B and 59D, however, when the head is provided with the write inductive head 83-1 and the read MR head 93-2, the gap position between the inductive head 93-1 and the MR head 93-2 differs. Hence, the variation in the yaw angle brings about especially a deviation of the track position of the MR head 93-2. Thus, it follows that a degree of mixing of adjacent track signal components among reading signals fluctuates depending on the respective tracks. A resolution of read data is thereby decreased.
For preventing this decline, a read output level is reduced by decreasing the gap width of the MR head 93 so that the gaps of the MR head 93-2 extends over the adjacent track in any tracks. For this reason, there arises a problem in which an S/N ratio increases, correspondingly. Further, according to the conventional method using the fan-shaped bearing, the actuator is a special one. Therefore, its structure becomes complicated, and, besides, the costs also increase.
Further, in such a construction of the disk enclosure that the base and the cover are separated up and down in the prior art, it is possible to support both ends of shafts of a spindle motor and the rotary actuator, and, therefore, a rigidity is comparatively high. However, since a degree of deformation due to variations in temperatures of upper and lower members is different, the shaft of the rotary actuator is easy to skew, with the result that an off-track readily takes place.
Similarly, as disclosed in Japanese Patent Laid-Open Publication No.4-232610, in the construction where the base and the cover are separated right and left, the base is formed with two openings, and hence the rigidity of the enclosure is low. Accordingly, the shaft of the rotary actuator is easy to skew, and therefore the off-track is readily produced.